It is well recognized in the literature relating to oil recovery methods that only a small percentage of the oil present in subterranean reservoirs or earth formations can be recovered by primary recovery methods, and some supplemental recovery method must be applied to the reservoirs to extract appreciable amounts of additional petroleum. Commonly used supplemental recovery methods include waterflooding and steam injection, and methods which show considerable promise for future use include micellar flooding and flooding with a surfactant fluid or solution. Many of these supplemental recovery methods employ relatively fresh, i.e. low salinity and low hardness water. When fresh water contacts formations containing appreciable amounts of certain types of clay minerals, particularly the bentonites or sodium montmorillonites, swelling of the clay minerals occurs and in many instances the net result of injecting fresh water into the formation is substantial loss of permeability such that further fluid injection is made more difficult or even rendered completely impossible.
The above described basic problem is well recognized by persons skilled in the art of oil recovery, and many treatments have been described in the literature applied to formations for the purpose of reducing the sensitivity of clay-containing formations to contact with fresh water with only limited success. The use of relatively high salinity brines may be undertaken for waterflooding purposes if such are available, although this is not completely satisfactory for several reasons. The presence of high levels of sodium and other monovalent cations in the injected brines may not induce immediate clay swelling to levels that is caused by fresh water, but the high sodium content actually increase the propensity for the water sensitive clays to swell on later contact with fresh water. Moreover, if surfactant waterflooding is to be applied, most commonly available and inexpensive surfactants are not tolerant of the high salinity brines, and so fresh water must ultimately be injected into the formation for the pupose of decreasing the formation water salinity so as to permit use of commonly employed surfactants such as petroleum sulfonate. Moreover, steam flooding is a very successful method of supplemental recovery, especially for viscous crudes, and steam injection into the formation necessarily causes contact between earth formation minerals and very fresh water, i.e. the steam condensate.
In view of the foregoing brief discussion, it can be appreciated that there is an essential need for a method for treating subterranean, clay-containing earth formations so as to permanently and irreversibly render the formation insensitive to subsequent contact with fresh water.